1. Statement of the Technical Field
The present invention relates to storage system caching and more particularly to the management of cached data in a storage system.
2. Description of the Related Art
The vast majority of network devices process device requests indiscriminately. That is, regardless of the identity of the requester or the type of request, each device request can be processed with equal priority. Given the exponential increase in network traffic across the Internet, however, more recent network-oriented computing devices have begun to provide varying levels of computing services based upon what has been referred to as a “policy based service differentiation model”.
In a policy based service differentiation model, the computing devices can offer many levels of service where different requests for different content or services which originate from different requesters receive different levels of treatment depending upon administratively defined policies. In that regard, a service level agreement (SLA) can specify a guaranteed level of responsiveness associated with particular content or services irrespective of any particular requester. By comparison, quality of service (QoS) terms specify a guaranteed level of responsiveness minimally owed to particular requestors.
The policy based service differentiation model is the logical result of several factors. Firstly, the number and variety of computing applications which generate requests across networks both private and public has increased dramatically in the last decade. Each of these applications, however, has different service requirements. Secondly, technologies and protocols that enable the provision of different services having different security and service levels have become widely available. Yet, access to these different specific services must be regulated because these specific services can consume important computing resources such as network bandwidth, memory and processing cycles. Finally, business objectives or organizational goals can be best served when discriminating between different requests rather than treating all requests for computer processing in a like manner.
As device requests flow through the network and ultimately, to a file system, storage systems provide the terminal point of data access. More particularly, in response to any data request originating in a network, a file storage device such as re-writable media ultimately physically retrieves the requested data. Accordingly, data caching components at all levels of the network, and particularly within storage systems, replicate data that ultimately can be physically retrieved from fixed storage. Like other elements of the network, however, in high request volume circumstances, response times attributable to fixed storage access can add considerable costs to the overall response time.
Presently, the policy differentiation model has been applied to higher-level intermediate network components, such as application servers, in order to provide varying levels of service to particular requestors. The policy differentiation model, however, heretofore has not been applied to lower-level terminal network components such as fixed storage. Primarily, the policy differentiation model has not been applied to terminal network components due both to the inability for fixed storage devices to provide selectably varying levels of service, and also to the inability of fixed storage to access the terms of a service policy. Thus, though the remaining contact points of the enterprise can provide differentiated service, storage systems provide uniform service to all requesters.